# Measuring and Validating the Actual Evaporation and Soil Moisture Dynamic in Arid Regions under Unirrigated Land Using Smart Field Lysimeters and Numerical Modeling

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. The Study Area

^{2}. It is surrounded by the Arabian Gulf from all directions except the south, where it shares a land border with Saudi Arabia. The country is very arid due to low rainfall, and is characterized by relatively low relief, with a maximum height of 103 m above mean sea level at Qurain Abu al-Bawl. The topography is characterized by land depressions formed due to salt dissolution/collapse and karstification. Soil cover is generally very poor due to arid conditions and the lack of clastic input since the last glacial maximum, except for land depressions where loamy soil is accumulated by runoff.

#### 2.2. Smart Field Lysimeters

#### 2.3. Lysimeter Data

#### 2.4. Lysimeters Calculations

^{2}. A one-kilogram increase in the leakage tank weight equals a one-liter volume of precipitation (assuming deionized water density) or 14.144 mm of rain. The leakage rate at a given time step n is:

_{w}(n) is the water tank weight at the time step n. Similarly, the precipitation rate P [mm] is the sum of the change in the lysimeter weight and the leakage water in the tank

#### 2.5. Unsaturated Flow Modelling

_{s}), the inflection point of the retention curve, and the residual soil moisture (θ

_{r}). These values were 0.41, 0.04, and 0.27, respectively. The saturated hydraulic conductivity was 1.48 cm/day. Van Genuchten (1980) [23] described the water retention model as follows:

_{s}is the saturated hydraulic conductivity, S

_{e}is the effective water content, and l is a parameter describing the pore structure. The parameter m is described before. By obtaining the saturated hydraulic conductivity, as well as the saturated and residual moisture content, the parameters n and α can be obtained.

#### 2.6. Hydrus 1D Model

_{r}is the relative hydraulic conductivity as a function of head and location, and K

_{s}is the saturated hydraulic conductivity. Table 1 lists the various parameters used in the Hydrus model.

#### 2.7. Model Boundaries

#### 2.8. Model Calibration

_{m}is the measured soil moisture in the field and θ

_{calc}refers to the calculations from Equation (5) at the n number of model nodes. To determine α and n, the measured values from the lab were fitted to the curve using the van Genuchten equation (Equation (5)). The fitting was based on least square, using an Excel spreadsheet [26]. The results show that α = 0.029 and n = 1.4.

## 3. Results and Discussion

#### 3.1. Temperature Fluctuation

#### 3.2. Soil Moisture

#### 3.3. Soil Moisture Dynamics

#### 3.3.1. November 2018

#### 3.3.2. December 2018 to March 2019

#### 3.3.3. April 2019

#### 3.4. Electrical Conductivity (EC)

#### 3.5. Water Balance Analysis of the Wet Season

#### 3.5.1. September 2018

#### 3.5.2. October 2018

Component | Value (mm) |
---|---|

Rainfall | 73.31 |

Leakage | 6.71 |

Evaporation | 29.39 |

Change in soil moisture | 35.21 |

Flow into lysimeter | 0 |

#### 3.6. Water Balance Analysis of the Dry Season

#### 3.7. Soil Matric Potential

#### 3.8. Model Results

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**Schematic chart of how the smart field lysimeter operates (created after UMS GmbH [22]).

**Figure 8.**Electrical conductivity of soil at T1 (5 cm), T2 (35 cm), and T3 (55 cm) for lysimeter 1 (

**a**) and lysimeter 2 (

**b**).

Parameter | Value |
---|---|

Number of soil layers | 1 |

Thickness of soil zone | 600 mm |

Time step | 1 day |

Heat flow | 0 |

Solute flow | 0 |

Root growth | 0 |

Upper boundary | Atmospheric |

Lower boundary | Free drainage |

Hysteresis | 0 |

Total running time | 30 days |

Soil saturation moisture content | 0.41 |

Soil residual moisture content | 0.05 |

Saturated hydraulic conductivity | 2.2 cm/d |

Component | Value (mm) |
---|---|

Rainfall | 19.52 |

Leakage | 2.22 |

Evaporation | 19.81 |

Soil moisture | −2.51 |

Flow into lysimeter | 0 |

Month | Evaporation (E) [mm] | Change in Soil Moisture ΔS [mm] | Rain (P) [mm] | Leakage (L) [mm] | Flow (F) [mm] |
---|---|---|---|---|---|

Sep | 3.24 | −2.53 | 0 | 0 | 0.71 |

Oct | 29.39 | 35.21 | 71.31 | 6.71 | 0 |

Nov | 19.81 | −2.51 | 19.52 | 2.22 | 0 |

Dec | 2.15 | −2.15 | 0 | 0 | 0 |

Jan | 2.34 | −2.34 | 0 | 0 | 0 |

Feb | 2.49 | −2.49 | 0 | 0 | 0 |

Mar | 3.9 | −3.9 | 0 | 0 | 0 |

April | 13.38 | −1.48 | 11.9 | 0 | 0 |

May | 5.98 | −5.17 | 0 | 0 | 0.81 |

June | 5.52 | −4.76 | 0 | 0 | 0.76 |

July | 5.12 | −4.3 | 0 | 0 | 0.82 |

August | 4.31 | −3.58 | 0 | 0 | 0.73 |

Total | 97.63 | 0.00 | 102.73 | 8.93 | 3.83 |

Month | Hydrus Evaporation (mm) | Lysimeter Evaporation (mm) |
---|---|---|

September 2018 | 3.59 | 3.24 |

October 2018 | 30.7 | 29.39 |

November 2018 | 18.13 | 19.81 |

December 2018 | 2.92 | 2.15 |

January 2019 | 2.53 | 2.34 |

February 2019 | 2.31 | 2.49 |

March 2019 | 3.62 | 3.9 |

April 2019 | 14.1 | 13.38 |

May 2019 | 6.10 | 5.98 |

June 2019 | 6.02 | 5.52 |

July 2019 | 4.20 | 5.12 |

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**MDPI and ACS Style**

Baalousha, H.M.; Ramasomanana, F.; Fahs, M.; Seers, T.D. Measuring and Validating the Actual Evaporation and Soil Moisture Dynamic in Arid Regions under Unirrigated Land Using Smart Field Lysimeters and Numerical Modeling. *Water* **2022**, *14*, 2787.
https://doi.org/10.3390/w14182787

**AMA Style**

Baalousha HM, Ramasomanana F, Fahs M, Seers TD. Measuring and Validating the Actual Evaporation and Soil Moisture Dynamic in Arid Regions under Unirrigated Land Using Smart Field Lysimeters and Numerical Modeling. *Water*. 2022; 14(18):2787.
https://doi.org/10.3390/w14182787

**Chicago/Turabian Style**

Baalousha, Husam Musa, Fanilo Ramasomanana, Marwan Fahs, and Thomas Daniel Seers. 2022. "Measuring and Validating the Actual Evaporation and Soil Moisture Dynamic in Arid Regions under Unirrigated Land Using Smart Field Lysimeters and Numerical Modeling" *Water* 14, no. 18: 2787.
https://doi.org/10.3390/w14182787